Flow control system for continuously delivering massecuite or the like



Dec. 14, 1965 R. c. GOODWIN 3,223,283

FLOW CONTROL SYSTEM FOR GONTINUOUSLY DELIVERING MASSECUITE OR THE LIKE Filed July 25, 1963 2 Sheets-Sheet 1 AIR IN INVENTOR RALPH C. GUODWIN ATT EY Dec. 14, 1965 R. c. GOODWIN 3,2

FLOW CONTROL SYSTEM FOR CONTINUOUSLY DELIVERING MASSECUITE OR THE LIKE 2 Sheets-Sheet 2 Filed July 25, 1963 INVENTOR RALPH C. GOODWIN OPEN GATE United States Patent 3,223,283 FLOW CONTROL SYSTEM FGR CGNTINUOUSLY DELlVERlNG MASSECUITE GR THE LIKE Ralph C. Goodwin, Hamilton, Ghio, assignor to The Western States Machine Company, Hamilton, Ohio, a

corporation of Utah Filed July 25, 1963, Ser. No. 297,547 8 Claims. (Cl. 222-56) This invention relates to a system for controlling the rate of flow of a stream of viscous liquid of semi-liquid material pouring continuously by gravity from a supply of the material that is subject to variations of its head pressure. It relates more particularly to such a system for continuously delivering a stream of a mixture of solids and liquid such as sugar massecuite from a supply tank to a continuous centrifugal machine for separation of the liquid and solid phases of the mixture.

In a typical continuous centrifugal installation as used in sugar manufacture a stream of the material to be processed is delivered continuously into a constantly rotating centrifugal basket in which the liquid phase of the material is purged away from the solid phase by centrifugal force while the solids are moved along the basket until discharged from it after a certain period of centrifugal treatment.

It is important to the efiiciency of the operations that the charge material be delivered into the basket at a substantially constant rate. Variations in the loading rate necessarily cause variations of the thickness or of the duration of treatment of the layer of solids in the basket and, therefore, in effects of the centrifugal treatment such, for example, as the purity of the separated solids and liquids discharged from the basket.

The charge material typically is delivered to the centrifuge by gravity flow from a pipe leading from a supply tank that holds a relatively large mass of the material. Whether the supply in the tank is replenished periodically or otherwise, the level and consequently the head of the material in the tank is subject to variations which result in varying pressures at the head of the stream flowing from the loading pipe or spout and, consequently, in objectionable variations of the note of gravity flow of the material into the centrifugal basket.

It is an object of the present invention to provide a system for continuously delivering a freely pouring stream of viscous liquid or semi-liquid material at a substantially constant rate of flow from a supply of the material that is subject to variations of its level or head pressure.

A more particular object is to provide a flow control system for loading a continuous centrifugal machine as used for the processing of a ilowable mixture of solids and liquid, such as a sugar massecuite or magma, whereby a stream of the material may be kept pouring into the centrifugal basket at a substantially constant rate notwithstanding variations of the level and consequently of the head of a supply of the material held in a tank serving the machine.

Another object of the invention is to provide a flow control system for such purpose which will act directly and immediately in response to variations of the level or head of the reserve supply of the charge material.

Further objects of the invention are to provide for convenient manual control of the rate of flow of the material and for automatic termination of all flow to the basket whenever required in the course of operations of the machine.

According to the present invention, a pipe or spout through which the viscous material is conducted from a supply tank is provided at its delivery end with an outlet orifice of the size required for pouring the desired stream of the material continuously by gravity to the point of reception, such as the basket of a centrifugal machine driven continuously at constant speed, and where the pipe or spout leads into the outlet orifice it forms a head chamber which has a larger cross sectional area than the orifice and which communicates with the supply tank through a gate valve that is normally held open at a position determined by and variable with the head or pressure of the material in the head chamber.

The gate of the gate valve determines the passage area through which the material will fiow and transmit pressure from the reserve supply held in the tank, so that a change of the gate position will vary that passage area and thereby vary the friction head loss occurring in the viscous material as it passes from the tank past the gate valve to the head chamber.

For a material of given flow qualities, the velocity of the stream pouring from the spout orifice will vary with the magnitude of the head or pressure acting upon the material in the head chamber. Accordingly, by the provision of means to sense variations of that head or pressure from a predetermined value corresponding to a desired rate of flow of the material from the orifice, and to vary the position of the gate in compensation for such variations, the head or pressure of the material in the head chamber and thereby the velocity as well as the size of the stream pouring from the outlet orifice are kept substantially constant notwithstanding variations of the level and head of the supply of the material held in the tank.

The foregoing and other objects, features and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof and from the accompanying illustrative drawings wherein:

FIG. 1 is a schematic view of a continuous centrifugal installation embodying a flow control system according to the invention; and

FIG. 2 is a diagrammatic view, partly in section, of pressure sensing and gate valve controlling elements of the system.

The centrifugal installation 10 shown in FIG. 1 includes a conical basket 12 that is rotated continuously within a stationary curb structure 13, being driven through belts 16 from a motor 14 supported outside the curb structure.

Charge material such, for example, as sugar massecuite, is delivered to the centrifugal basket in a stream S pouring continuously by gravity from an outlet orifice 22 at the delivery end of a spout 24 connected with a massecuite supply tank 20.

The supply tank 2% holds a body of the massecuite that is large in relation to the amount being processed in the basket at any moment. As the material flows from the spout orifice, the level of the body M in the tank gradually recedes until the supply is exhausted or replenished. Replenishment is usually effected by the delivery of freshly crystallized massecuite into the tank through an intake, such as chute 26, from a vacuum pan or from a crystallizer in the case of lower purity materials.

The variations of level which occur in the tank are, of course, attended by variations of the pressure head tending to force the material through the spout. These ordinarily bring about quite objectionable variations of the velocity of the stream of the material pouring into the centrifugal basket.

Such variations of the flow rate may be prevented according to the invention, notwithstanding the continuation of supply level and head variations in the tank, by

sensing the pressure of the massecuite in a head chamber 23 formed by the spout 24 just ahead of the outlet orifice 22 and utilizing sensed variations in this pressure to vary compensatingly the extent of opening of a gate Valve 30 which is disposed across the spout so as to define a restricted entrance passageway of variable size leading from the tank into the head chamber. The gate valve may be, for example, one of known construction such as a 6" No. 392 DeZurik bonnetless knife gate valve.

In order to insure that the head chamber 23 will always be full of massecuite under a sensible pressure causing a full stream of the material to pour from the orifice 22 into the basket, this chamber is formed with a diameter or cross sectional area considerably greater than that of the outlet orifice 22.

The gate valve includes a sliding gate 32 that is positioned andmovable by a rod 34 connecting it with the piston 35 of a double-acting fluid pressure cylinder 36. The cylinder 36 has ducts 37 and 38 leading respectively into its outer and inner ends for conducting to and from these ends a suitable fluid under pressure, for example, compressed air, by which the piston 35 and thereby the gate 32 are positioned as required.

The position and action of the gate are controlled automatically through a diaphragm-operated servo valve systern 40, or manually whenever desired through a manual control system 80 which has an automatic gate closing control 100 associated with it.

For automatic control of the loading rate by the servo system, the pressure of the massecuite in the head chamber 23 is sensed at all times by a relatively large area diaphragm 42 which is mounted across an opening 25 formed in the rigid wall of the chamber. The diaphragm thus is always exposed to and positioned by the pressure of the massecuite in the head chamber. In the arrangement shown, it is clamped at its periphery between a removable clamping ring 43 and a mounting flange 26 formed around the opening 25, and a plate 44 bearing against its outer side takes positions corresponding to those of the diaphragm.

The diaphragm plate is formed centrally with a hollow cup 46 which receives and positions a collar 47 on the lower end of a valve spool 48. This valve spool constitutes the moving element of a five-way servo valve, the body 50 ofwhich is fixed through a centrally apertured adapter plate 51 to the clamping ring 43. The adapter plate and the valve form a unit that is removable from the ring 43 and spout 24 for maintenance without removal of the diaphragm 42, hence without need for shutting off the flow of massecuite through the spout.

At its end disposed away from the diaphragm the valve body 50 supports a hollow extension 70 which houses a compression spring 72 bearing at one end against a collar 49 formed on the upper end of the valve spool 48 and bearing at its other end against the end of a knurled cap 74 threaded on the end of extension 70. By rotation of the cap 74 the degree of compression of the spring 72 can be adjusted so as to pre-set or adjust the force with which the spring acts through the valve spool 48 to press the diaphragm 42 against the massecuite in the head chamber in opposition to the pressure exerted on the diaphragm by the massecuite.

The valve body 50 has a central intake port 52 connected through tubing 53 with a source of compressed air or other suitable fluid under pressure. It also has pressure ports 54 and 56 connected respectively through ducts 55 and 57 with the ducts 37 and 38 of cylinder 36, and two vent ports 58 and 59. The vent ports are provided with restricted orifice devices 58a and 59a, preferably adjustable in orifice size, to restrict the rate of exhaustion of fluid pressure through them.

The valve spool 48 is formed with land portions 60 and 62 which coact with the ports 54 and 56 to close or open the valve. When the spool is in a neutral position, the land portions close those ports and block all 'passage of fluid through the valve. If then the pressure head of massecuite bearing against the diaphragm 42 exceeds the force of spring '72, the spool 48 is moved a short distance to establish communication within the valve body between the air inlet port 52 and pressure port 54, and between the pressure port 56 and vent port 59. Fluid under pressure from the tubing 53 is then passed through the valve and through ducts 55 and 37 to the outer end of the cylinder 36, so as to displace the piston 35 and gate 32 in the direction to reduce the passage area through the gate valve, while fluid pressure is exhausted from the inner end of the cylinder through ducts 38 and 57, pressure port 56 and restricted vent port 59.

Similarly, if the pressure head acting on the diaphragm falls below the force of spring 72, the spool 48 is moved a short distance toward the massecuite in chamber 23, to pass fluid under pressure through port 56 and ducts 57 and 38 to the inner end of the pressure cylinder 36 while exhausting pressure from the outer end of the cylinder through ducts 37 and 55, port 54 and restricted vent port 58. The piston 35 and gate 32 are then displaced in the direction to increase the passage area through the gate valve.

The force applied by the spring 72 counter to the massecuite pressure tending to move the diaphragm 42 against the spring thus becomes a measure of the pressure maintained in the head chamber and, therefore, assuming the flow qualities of the material to be uniform and the orifice 22 to be of suitable size, the spring force will determine the velocity of the stream of massecuite pouring continuously from the orifice 22 into the centrifugal basket.

When that pressure tends to increase, as when the supply of massecuite in tank 20 is being replenished, the gate 32 is moved correspondingly to decrease the passage area through the gate valve and thereby increase the friction head loss of the massecuite passing through that valve into the head chamber, until the massecuite pressure acting on the diaphragm in the head chamber again has the value that balances the preset spring force. The gate motion then stops.

Conversely, when the pressure in the head chamber tends to decrease, as occurs through the gradual fall of the massecuite level in the tank 20 as material is delivered from the spout 24, an incremental displacement of the servo valve results to cause an incremental gate opening movement that decreases the friction head loss of the massecuite passing through the gate valve until the spring force is again balanced by the massecuite in chamber 23.

It will be evident that the stream S pouring from the orifice 22 is at substantially atmospheric pressure and that its velocity is variedwith variations in the pressure maintained in the head chamber 23 leading into the outlet orifice, which pressure is set at a value that Will give the required rate of flow through the orifice and yet will be considerably lower than the pressure induced by the head of material in the tank 20 at all times except when the tank is nearly empty. The difference of pressures, or pressure drop, between the upstream end of the spout 24 and the head chamber 23 is maintained by restriction of the flow of the massecuite through the gate valve 30 and is varied from time to time, as required to keep the pressure in chamber 23 substantially constant, by adjustments of the position of the gate valve.

Since sugar massecuite is usually highly viscous, the pressure sensed in the head chamber changes rather slowly upon variation of the passage area of the gate valve. It is important, therefore, that the displacement of the gate 32 be slow, in order to avoid over-correction and hunting of the control system. For this purpose, the compressed air supply line 64 leading to the tubing 53 and the servo valve may be constricted, as by providing in that line an adjustable needle valve 66 such, for example, as a Beckett Harcum A control valve No. FCV 2000 B;

and the motion of the piston may be retarded by constricting the flow of pressure fluid out of either end of the cylinder 35. The latter function is achieved by the restricted orifice devices 58a and 59a in the vent ports 58 and 59 of the servo valve.

The action of those devices may be preceded, especially for purposes of the manual control system 80 presently to be described, by providing in each of the cylinder ducts 37 and 38 a valve 68 that will constrict the flow of fluid from either end of the cylinder and yet allow free flow of the pressure fluid into the cylinder. Each valve 68 may be, for example, an adjustable Pneu-trol needle check valve.

The collars 47 and 49 on the ends of the valve spool 48 are arranged in closely spaced relation to the ends of the valve body 50 so that the valve spool can travel only a very small distance, for example of .025", to either side of its neutral position. It will be evident that rotation of the cap 74 will vary the preloading of the spring 76 and thereby vary within a certain range the pressure to be maintained in the head chamber 23 and the velocity of the stream pouring from the outlet orifice 22. A stop screw in the lower end of the cap '74 cooperates with a shoulder on the extension 70 to limit the outward movement of the cap and thereby insure that the spring will always be under at least a predetermined minimum compression suiricient to keep the gate valve open, or cause it to open further in the absence of diaphragm pressure, so that massecuite will pour from the spout at all times during normal operations.

It the rate of flow required for the basket 12 is not provided within the range of velocity adjustments available by rotation of the cap 74, it may be so provided by suitable selection of the size of the outlet orifice 22. For example, a bushing may be inserted in the discharge end of the spout 24 to reduce the etlective size of the outlet orifice. The outlet orifice in any case is to be of a size that will run full so as to maintain a sensible pressure in the head chamber 23 at all times.

The manual control system 88 is provided to enable an attendant of the installation to control the flow of massecuite into the centrifuge manually whenever desired. For this purpose, a manually operable 5-way control valve is provided on a branch 82 from the compressed air supply line 64 and is connected through ducts 83 and 84 with the ducts 55 and 57 leading to the outer and inner ends, respectively, of the gate valve operating cylinder 36. The manually operable valve includes a multi-port valve body 85 having a valve spool 86 slidably fitted therein. An eccentric pin 89 on the hub of a pivotally mounted handle 88 engages spaced collars 87 and 91 on the lower end of the spool so that the spool is movable, by selective pivotal movement of the handle, to neutral, gate opening, and gate closing positions. Springs Qt) hearing against the opposite ends of the spool normally hold the spool in its neutral position and automatically return the spool to that position from either of its extreme positions upon release of the handle 83.

In the neutral position of the valve spool, land portions 92 and 94 on the spool close oli pressure ports 93 and 95 connected with the ducts 83 and 84 and block all passage of fluid through the valve body 85.

When the control handle 88 is turned upward the spool is moved farther into the valve body, to a gate closing position. The pressure fluid in branch line 82 then passes through port 93 and ducts 83 and 37 into the outer end of the cylinder 36, while the inner end of the cylinder is vented at a limited rate through duct 38, flow restrictor 68, duct 84, pressure port 95 and a vent port as in body 85. The gate 32 is thus moved to reduce the passage area of gate valve 323, by action overriding that of the servo valve system 4%.

Similarly, the gate 32 is moved to increase the passage area of the gate valve when the control handle 88 is turned downward. The spool 86 then is moved from its neutral position to a gate opening position in which pressure fluid from the branch line 82 passes through port 95 and ducts 8-4- and 33 into the inner end of the cylinder 36 while the outer end of the cylinder is vented at a limited rate through duct 37 and its flow restrictor, duct 83, pressure port 93 and a vent port 97.

If the manual control system 80 is operated while the supply of fluid pressure to the servo valve system 40 is cut off, as by a globe valve 93 between line 64 and the tubing 53, the massecuite or gate valve 30 will remain Wherever the attendant positions it by manipulation of the hand lever 88. On the other hand, if the globe valve is open the massecuite flow continues to be controlled automatically by the servo valve system, but its'action may be overridden at any time by the manual control system 80. When the handle 88 is returned to neutral position after a movement to adjust the position of gate 32, the servo valve system will resume control of the massecuite flow.

It is important that the delivery of massecuite to the entrifugal machine be stopped upon the occurrence of any of various abnormal conditions, such as a power failure, an overloading of the basket, a stopping of the machine, or others. The automatic gate closing control 160 is provided for this purpose.

As seen in FIG. 2, the inner end of the valve spool '86- of the manual control system carries a piston 102 slidable in a chamber 104- located at the end of valve body 35. A pressure fluid duct 105 leads into that chamber, at a location beneath the piston, from the outlet side of a suitable control valve such as a solenoid valve 106. A fluid pressure line 167 leading into the inlet side of this valve supplies a suitable fluid under pressure, such as compressed air, to the valve at all times.

During normal operations of the centrifugal installation the valve 1436 is held closed, as by keeping its solenoid energized, so that no pressure fluid will flow through it to the piston chamber 104. Whenever the solenoid is deenergized, however, as by the opening of a control cir cuit to it upon the occurrence of an abnormal or hazardous condition, fluid under pressure from line 107 passes immediately through valve 106 into chamber 104 and moves the valve spool 86 fully to its gate closing position. The pressure then admitted into the outer end of cylinder 36 moves the massecuite valve gate 32 to its completely closed position, thus stopping all flow from the loading spout.

While the principles of the present invention and particulars of a preferred way of carrying it into practice have been described hereinabove and illustrated in the accompanying drawings, it will be evident that numerous variations and substitutions may be made by those skilled in the art without departing from the substance or contribution of the invention, which is intended to be defined by the appended claims.

What is claimed is:

1. Apparatus for delivering viscous liquid material in a stream pouring at a substantially constant rate from a supply source wherein the head pressure of the material is subject to variations, comprising:

a spout for conducting the material from said source under the head pressure of the supply therein, said spout having at its outlet end an orifice that forms a pouring stream of the material of the required size, and defining upstream of said orifice a head chamber of substantially greater cross sectional area than said orifice,

a displaceable gate in said spout at the upstream side of said chamber for continuously constricting the flow of the material into said head chamber so as to maintain the pressure of the material in said chamber below said head pressure,

means outside said spout and insensitive to the velocity of said flow for positioning said gate, and normally holding said gate sufliciently open to keep said chamber full of the material under pressure,

and means operative in response to a variation of said head pressure for actuating said positioning means and causing the same to vary correspondingly the extent of opening of said gate so as to keep the pressure of the material in said chamber and thereby the velocity of said stream substantially constant.

2. An apparatus for delivering viscous liquid material in a stream pouring at a substantially constant rate from a supply tank wherein the head pressure of the material is subject to variation, including:

a spout for conducting the material from the tank under the head pressure of the supply therein, said spout having at its outlet end an orifice that forms a pouring stream of the material of the required size, and defining upstream of said orifice a head chamber of substantially greater cross sectional area than said orifice,

a displaceable gate in said spout at the upstream side of said chamber for continuously constricting the flow of the material into said head chamber so as to maintain the pressure of the material in said chamber below said head pressure,

means outside said spout and insensitive to the velocity of said fiow for positioning said gate, and normally holding said gate sufiiciently open to keep said chamber full of the material under pressure,

means in said chamber for sensing the head of the material therein,

and means controlled by said sensing means and responsive to a deviation of said head from a predetermined value for actuating said positioning means and causing the same to vary the extent of opening of and thereby the pressure drop across said gate so as to keep said head and the velocity of said stream substantially constant.

3. Apparatus for delivering viscous liquid material in a stream pouring at a substantially constant rate from a supply tank wherein the head pressure of the material is subject to variations, including:

a spout for conducting the material from the tank under the head pressure of the supply therein, said spout having at its outlet end an orifice that forms a pouring stream of the material of the required size, and defining upstream of said orifice a head chamber of substantially greater cross sectional area than said orifice,

a gate in said spout at the upstream side of said chamber for continuously constricting the flow of the material into said head chamber so as to keep the chamber full of said material yet under a pressure lower than said head pressure,

a reversible motor positioning said gate,

a diaphragm in said chamber for sensing the pressure of the material therein,

a controller connected with said motor and having an element movable in opposite directions to energize said motor for opening and closing movements, respectively, of said gate,

said controller element being connected with said diaphragm and biased by the same in gate closing direction by the pressure of the material in said head chamber,

and yieldable means continuously applying to said controller in opposition to such pressure a predeterrnined force urging the element in gate opening direction,

whereby the pressure in said chamber and thereby the velocity of said stream may be kept substantially constant at values determined by the magnitude of sa d fo ce,

4. Apparatus for delivering a stream of massecuite continuously from a supply tank into the basket of a constantly rotating continuous centrifugal machine, comprising:

a spout extending from the bottom of the tank and provided at its delivery end with an outlet orifice from which a stream of the massecuite of the required size will pour continuously by gravity into the basket, said spout defining upstream of said orifice a head chamber of substantially greater cross sectional area than said orifice,

a gate in said spout between said head chamber and the tank for continuously constricting the flow of the massecuite into said chamber,

motor means positioning said gate and normally holding it open to a limited extent sufficient to keep said head chamber full of massecuite under pressure lower than the head pressure of the supply upstream of the gate, said motor means being operable in opposite directions to decrease and increase, respectively, the extent of opening of and thereby the pressure drop across said gate, and

control means for governing the operations of said motor means.

5. Apparatus according to claim 4, said control means including a servo control system operative in response to a variation of said head pressure to vary correspondingly the position of said gate so as to keep the pressure of the massecuite in said head chamber and thereby the velocity of said stream substantially constant.

5. Apparatus according to claim 4, said control means including a servo control system operative in response to a variation of said head pressure to vary correspondingly the position of said gate so as to keep the pressure of the massecuite in said head chamber and thereby the velocity of said stream substantially constant and a manual control system for operating said motor means in either of said directions in overriding relation to said servo control system.

7. Apparatus according to claim 4, said control means including a servo control system operative in response to a variation of said head pressure to vary correspondingly the position of said gate so as to keep the pressure of the massecuite in said head chamber and thereby the velocity of said stream substantially constant and means operative in overriding relation to said servo control system to cause said motor means to close said gate upon the occurrence of an abnormal condition in the operations of the centrifugal machine.

3. Apparatus according to claim 4, said motor means including a double acting fluid pressure cylinder containing a piston connected with said gate and having ducts for fiuid under pressure leading into opposite ends of the cylinder, said control means including a valve normally blocking flow of such fluid through said ducts but movable to supply such fluid into either of said ends while releasing such fluid from the other of them and means for constricting the flow of fluid from either of said ends so as to retard displacements of said piston and said gate.

References Cited by the Examiner UNITED STATES PATENTS 2,375,914 5/1945 Gardineer et a1. 137-488 X 2,612,182 9/1952 Luster 137-505.39 2,687,740 8/1954 Iarund 222-56 X 3,104,030 9/1963 Hewlett 222-56 X LOUIS l. DEMBO, Primary Examiner. HADD 5. LANE, Examiner, 

1. APPARATUS FOR DELIVERING VISCOUS LIQUID MATERIAL IN A STREAM POURING AT A SUBSTANTIALLY CONSTANT RATE FROM A SUPPLY SOURCE WHEREIN THE HEAD PRESSURE OF THE MATERIAL IS SUBJECT TO VARIATIONS, COMPRISING: A SPOUT FOR CONDUCTING THE MATERIAL FROM SAID SOURCE UNDER THE HEAD PRESSURE OF THE SUPPLY THEREIN, SAID SPOUT HAVING AT ITS OUTLET END AN ORIFICE THAT FORMS A POURING STREAM OF THE MATERIAL OF THE REQUIRED SIZE, AND DEFINING UPSTREAM OF SAID ORIFICE A HEAD CHAMBER OF SUBSTANTIALLY GREATER CROSS SECTIONAL AREA THAN SAID ORIFICE, A DISPLACEABLE GATE IN SAID SPOUT AT THE UPSTREAM SIDE OF SAID CHAMBER FOR CONTINUOUSLY CONSTRICTING THE FLOW OF THE MATERIAL INTO SAID HEAD CHAMBER SO AS TO MAINTAIN THE PRESSURE OF THE MATERIAL IN SAID CHAMBER BELOW SAID HEAD PRESSURE, MEANS OUTSIDE SAID SPOUT AND INSENSITIVE TO THE VELOCITY OF SAID FLOW FOR POSITIONING SAID GATE, AND NORMALLY HOLDING SAID GATE SUFFICIENTLY OPEN TO KEEP SAID CHAMBER FULL OF THE MATERIAL UNDER PRESSURE, AND MEANS OPERATIVE IN RESPONSE TO A VARIATION OF SAID HEAD PRESSURE FOR ACTUATING SAID POSITIONING MEANS AND CAUSING THE SAME TO VARY CORRESPONDINGLY THE EXTENT OF OPENING OF SAID GATE SO AS TO KEEP THE PRESSURE OF THE MATERIAL IN SAID CHAMBER AND THEREBY THE VELOCITY OF SAID STREAM SUBSTANTIALLY CONSTANT. 